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B. 0. WILLIS.

TELEPHONE RECEIVER. APPLICATION vFILED AUG-25, H513.

Patented Aug. 16, 1916.

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TELEPHONE RECEIVER.

APPLICATION FILED AUG-25, 1913.

Patented Aug. 15 1916.

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v TOE L BERNARD n. WILLIS, or CHICAGO, ILLInoIs, Assmnon 'IO AUTO ATIC nLEc'rnIc COMPANY, or cnrcaso, ILLINOIS,'IA conPoRArIoN or ILLINOIS.

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To atl whom it mag concern:

Be it known that I, BERNARD D. WILLIS, a

citizen of the United States of America, and

resident of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Telephonetype of receiver in which the constant mag-- netism of the receiver is furnished by an electromagnet, no permanent magnets'being employed in the receiver. Receivers otfthis character are usually connected in series in the line, and the current for supplying the magnetism is furnished from the central office. The sensitiveness of a receiver varies with its inductance, which in turn depends upon the strength of the energizing cur-' rent. The most sensitive telephone receiver is one in which a given change of current (for example one milliampere) produces the greatest deflection in'the diaphragm. This deflection is proportional to the change in pull exerted by the electromagnet upon the diaphragm. The-pulldepends uponthe strength of the magnetic flux produced by the current flowing through the coil. The amount of magnetic flux produced by the current is not necessarily proportional to the current. The ratio of magnetic flux to current, first increases with increasing current arriving at a maximum and then decreasing as the current becomes still greater. At the point of greatest ratio the given change in current (for example one milliampere) pro duces the greatest change in magnetic flux and hence the greatest change of pull on the diaphragm. Therefore atthis-point the receiver is most sensitive. Inductance and permeability are proportional to the ratio of magnetic flux to the current producing it. Hence inductance and permeability arrive at a maximum simultaneously with the ratio of flux and current. Thus it is that the sensibility in a telephone receiver is marked by large inductance.

The object of my invention is, therefore, to provide a receiver in which the maximum inductance is produced by the weakest current which is met with in practice-that is,

the current which is received over the lon .v

gest line by which the receiver will be usedwhich inductance decreased with the in Specification of Letters Patent. Patented Aug. 1L5, 19168. Application filed August 25, 1913. Serial No. 786,588.

crease of the energizing current within the ordinary limits.

In the accompanying drawings I have illustrated one formof my invention.

In these dra'wingsFigure 1 is a longitudinal section of a telephone receiver embodying the principles of my invention. Fig. 2 isan end view of the same withthe cap and diaphragm removed. Fig. 3 is an.

enlarged perspective view of the soft iron shell of the electromagnet. Fig. 4 is a detail view of the mounting or connection fitting by which the circuit conductors are connected with the coils of the receiver. Fig. 5 is a diagram of a telephone circuit, illustrating the manner in which the receiver forming the subject matter of the herein disclosed invention may be connected to the line and supplied with energizing current from the central ofiice battery. .In Fig. 6 are shown curves showing the relation of the magnetic and electrical properties of difi'erent receivers.

As illustrated in the drawings, it will be seen that my receiver comprises the usual shell 0 and cap -D, which maybe of any suitable form. In the lower or enlarged end of the shell C there is a non-magnetic cup A which is provided with a flanged edge a which is clamped between the shell C and the cap D, whereby the cup is held firmly in place. ceiver comprises a coil of wire E wound upon a soft. iron core" 6 and mounted inside a soft iron cup or, shell 6. The electromagnet is secured to the bottom of the cup A by means of the screw e The diaphragm B is clamped in place betweenthe cap D and the fiangeaof the cup A. To the back of the cup A there. is secured a terminal blockcomposed of insulating material and carrying the binding .posts f The block isheld in pi'ace by the screws j and f which pass through the block and into the back of the cup. The binding posts f are provided with clamping screws f for holding the terminals of the receiver cord and with projecting portions i which extend through openings in the back of the cup A, where they may be connected to the terminals of the coil. i

. The electromagnet which acts upon the diaphragm ofa receiver shouldhave a cer tain amount of constant magnetism in which fluctuations maybe produced by the vary- The, electromagnet of the recrease indefinitely with the increase of themagnetizing force, but rises to a maximum value and then slowly decreases. Therefore, in order to produce the most sensitive receiver of the kind shown herein, which is dependent for its constant energization upon the current which is supplied to.the telephone over the line circuit from the central oflice battery, the electromagnet of the receiver should be so constructed and proportionedthat 'the maximum inductance islattained by the current which is thus supplied to the telephone from the central oflice. Since in a telephone system all lines cannot be supplied with exactly the same amount of current on account of their unequal length'and resistance, I have d1scovered thatthe most efficient results can be obtained by constructing the magnet to work above the knee of the B I-I curve of the receiver, so that the maximum inductance will be produced by approximately the minimum current which the receiver will receive 1n practice. Thisls desirable for two reasons. First, the maximum inductance being produced by the minimum current used,

- rather than by the'maximum current, the

sensitiveness of the receiver will increase, instead ofdecrease, wlth the increase 1n the length of the line andtconsequent decrease 4Q of current. Second, there is a greater working margin as to the length of the line, since the slope of the curve above the knee is smaller than below and the range between the-[longest and the shortest linesv is increased. The first feature,.itis evident, is very desirable, because the longer the line received by the receiver.

ceiver constructed to give the results dis cussed above. By reference to this curve it will be seen that the maximum inductance occurs when the magnetizing current is at the minimum limit of the useful energizing imatelythe maximum current which will be used in the usual telephone receiver. With this constructionthe sensitiveness of the receiver when theminimum current is employed is greatly increased. Thus thev operation of the receiver is rendered much more effective. In the curves 2, 3 and 4, which were plotted from ordinary receivers at present in commercial use, the inductance is much lower and increases continuously with the increase of current within the useful limits, so that the sensitiveness of these receivers, when used upon a. long line, is less than when used upon a short line. Therefore their efliciency isgreatly reduced. From this it will be seen that I have devised a very efiicient form of receiver and one which gives highly eflicient commercial results.

, lVhile I have illustrated in the drawings one particular form of receiver, itis, of course, to be understood that I am not limited to the exact construction shown.

What I claim as my invention is 1. In combination in a receiver, a coil, and a magnetic circuit including a receiver diaphragm associated with said coil, the said coil so wound and the magnetic circuit so proportioned that with an energizing current below the strength of one tenth (.10) ampere the inductance reaches a maximum. e 2; In combinationin a receiver, a coil, and a magnetic circuit including a receiver diaphragm associated with said coil, the

, said coil so wound and the magnetic circuit so proportioned that with an energizing current below the strength of one tenth (.10) ampere the inductance reaches a maxi- I mum, and with a stronger magnetizing current the inductance will be lower.

3. In combination in a receiver responsive the core of the electromagnet, which core and diaphragm are so constructed and proportioned and the coil so wound that the inductance of said receiver is greater with a current of one strength of flow than with a g 1 current of a greater-strength of flow. the more feeble will be the voice currents" 4. In combination in a receiver responsive I to talking current, a diaphragm and anelec- In Fig. 6 I haveshown a curve (curve No.- 1),.illustrat ing diagrammatically the rela-- 'tion of the current and inductance of a re tromagnet, an electromagnetic circuit for said receiver including said diaphragm and the core of the electromagnet, which core and diaphragm are so constructed and proportioned and which coil so wound that the inductance .of said receiver is greatest with a current strength below one tenth (.10) ampere' 5. In combination in a receiver responsive to talking current, a diaphragm and an elec- Itromagnet, an electromagnetic circuit for said receiver including said diaphragm and the core of the electromagnet, which core and diaphragm are so constructed and proportioned andwhich coilso wound that the inductance of said receiver is greatest with a current strength below one tenth (.10)

ampere and less with a greater current 6. In combination in a receiver responsive to talking current, an electromagnetic circuit, a coil, said coil associated with said electromagnetic circuit, said circuit so constructed and proportioned and said coil so wound that the inductance of said receiver is greatest with a current strength below one tenth (.10) ampere and less with a greater current flow. I

7 In combination in a receiver, a coil, and a magnetic circuit including a receiver diaphragm associated with said coil, the said coil so wound and the magnetic circuit so proportioned that with an energizing current below the strength of one tenth (.10) ampere the permeability reaches a maximum.

8. In combination in a receiver, a coil and 'a magnetic circuit including a receiver diaphragm associated with said coil, the said coil so wound and the magnetic circuit so proportioned that With an energizing current below the strength of one tenth (.10) ampere thev permeability reaches a maximum, and with a stronger magnetizing current the permeability will be lower.

9.. In combination in a receiver responsive,

to talking current, a diaphragm and an electromagnet, an electromagnetic circuit for said receiver including said diaphragm and the core of the electromagnet, which core and diaphragm are so constructed and proportioned and which coil so wound that the permeability of said'receiver is greatest with a current strength below one tenth (.10) ampere. Y

10. In combination in a receiver responsive to talking current, a diaphragm and an electromagnet, an electromagnetic circuit for said receiver including said diaphragm and the core of the electromagnet, which core and diaphragm are so constructed and circuit, a coil, said coil associated with said electromagnetic circuit, said circuit so constructed and proportioned and said coil so wound that the permeability of said receiver is greatest with a current strength below one tenth (.10) ampere and less with a greater current flow.

12. In combination, a microphone transmitter and a receiver responsive to talln'ng currnt passing through said transmitter,

said receiver comprising a magnetic circuit including a diaphragm and an electromagnet coil, said coil being sowound and the magnetic circuit so proportioned that with an energizing current below the strength of said talking current the permeability reaches a maximum.

13. The combination of a circuit, of a microphone transmitter, a receiver and a source of energy for said transmitter, a current in said circuit controlled by said transmitter, said receiver comprising a magnetic circuit including a diaphragm and an electromagnet coil, said coil being so wound and the magnetic circuit so proportioned that as the energizing current decreases the permeability of the receiver increases. Signed by me at Chicago, Cook county Illinois, this 20th day of August, 1913. BERNARD D. WILLIS.

Witnesses:

ALBERT ANDERSEN, H. E. HERSHEY. 

